I. This invention pertains to the field of thermally responsive clutch devices.
II. Within the prior art it is known to have clutches that respond to a predetermined temperature to connect or disconnect the drive mechanism. In particular for example, U.S. Pat. No. 2,381,567 discloses a clutch actuating device for a fan mechanism in which a temperature responsive spring will act to engage the clutch when a predetermined temperature is exceeded. None of the devices in the prior art provide a reasonable solution to having a clutch operate only within a predetermined desired temperature range. In particular, the prior art presents complicated solutions involving hydraulic and electric clutches to engage and disengage when desired. Further, the majority of the prior art uncovered with regard to this invention, relates to devices for driving a vehicle fan or cooling device in which provision is made to engage the drive of the fan only when a predetermined temperature is exceeded.
It has been found that one of the needs in the field of accessory drives for vehicle engines, and in particular, drives to an air conditioning compressor for a vehicle, it is desired to operate such compressor only within a desired temperature range. When the range is exceeded it is an indication serious trouble has developed, as for example, loss of lubrication which will destroy the compressor and the drive must be disengaged immediately. In addition, a simple device is required to provide for disengagement of the drive to the compressor when the temperature is below the given range, since at this time it is unnecessary to drive the compressor since the passenger compartment will not need cooling, and a certain amount of inefficiency otherwise results even when a controlled displacement is used.